1. Technical Field of the Invention
The present invention relates to a method of measuring the water content of charges in a shaft furnace, such as a blast furnace, for example.
The invention can be applied to shaft furnaces in general, the following description being based on blast furnaces for the sake of clarity and thus should not be construed in a limiting manner.
The operation of a shaft furnace such as a blast furnace may be simplified to a large extent by taking into account the fact that, on the one hand, a charge composed of ores and coke--these are discharged in such a way that they form superposed layers--is introduced at the top and, on the other hand, that at the bottom there are injected oxidants and fuels suitable for stimulating the reduction of the ore; while this reaction occurs reloading is performed as required.
It can be easily understood that the control of the blast furnace requires familiarity both with the chemical nature and the physical state (water content, size grading . . . ) of the various elements which are introduced thereinto.
Furthermore, it is understood that the regulating of the operations of the blast furnace is the more reliable, the greater the accuracy of the data regarding the characteristics of the products charged.
Currently one of the problems is in determining as accurately as possible the water content of the charged materials and in particular that of the coke.
2. Description of the Prior Art
Among the existing measuring methods the most common can be classed in two broad categories: on the one hand, those making use of neutron backscatter probes and, on the other, those based on infrared rays.
The apparatus in the first category, i.e. with neutron backscatter probes, are generally placed at weighing hoppers through which the material passes before being taken up by a device which raises it to the top of the blast furnace.
In the particular case of coke, the degree of inaccuracy is at least plus or minus 1%, which is high when it is considered that the humidity of coke often only varies between 2 and 8%. The measurements are falsified, on the one hand, by the fact that these apparatus react by measuring all the hydrogen contained in the material and are therefore affected not only by the water, but also by the carbonates, hydrocarbons, volatile materials, etc. present in the charge examined, and, on the other hand, by the fact that the measurement is taken in the weighing hopper, and thus it should be taken very rapidly since the coke charge does not remain there for very long; this results in a lack of counting time, i.e. an error resulting from the statistical nature of the measuring process.
The second category comprises the apparatus which use the principle of infrared sensors. These sensors are disposed in such a manner that they examine the material, for example when it is conveyed on belts, and measure by picking up the rays reflected by the material. The degree of inaccuracy is at least 1.5%. The measuring process is greatly affected by, and is therefore dependent on, the size grading, color, visible or "apparent" surface, etc., and in fact only measures the humidity of the surface.
It is known that at present the working processes in blast furnaces and therefore in shaft furnaces in general utilize various devices which analyze not only the charge products (coke, ores . . . ) and the injected elements (forced air, hydrocarbons, coal . . . ) but also the products discharged from the blast furnace, such as the gases collected in the blast furnace throat.
The applicant has observed an unexpected effect, i.e. that by carefully combining various operations for measuring the characteristics of the products entering and leaving the blast furnace, it is possible to calculate therefrom the water content of the charges, for example of the coke, without this water content itself actually being measured. This observation is the basis of the method of the present invention.